Calcium significantly reduces iron absorption
Calcium can reduce iron absorption by up to 50%. This is one of the most significant mineral interactions.
Take iron supplements away from calcium-rich foods or supplements.
Separate by at least 2-4 hours
Calcium significantly reduces iron absorption. Take iron supplements away from calcium-rich foods or supplements.
Separate by at least 2-4 hours
This interaction is rated “Warning” by Formulate. Calcium can reduce iron absorption by up to 50%. This is one of the most significant mineral interactions.
Studies from our registry that mention both calcium and iron. Each links to the primary source and the other Formulate pages citing it.
Both substances · 2010
Iron bioavailability and dietary reference values
Hurrell R, Egli I · American Journal of Clinical Nutrition
Reviews enhancers (vitamin C, meat) and inhibitors (phytate, polyphenols, calcium) of non-heme iron absorption, providing the mechanistic basis for pairing iron with vitamin C and separating it from tea/coffee.
Both substances · 2000
Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability
Hallberg and Hulthén · American Journal of Clinical Nutrition
Foundational model for non-heme iron absorption factoring vitamin C, phytates, tannins, and calcium interactions.
Mentions iron · 2017
Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women
Stoffel NU, Cercamondi CI, Brittenham G, et al. · Blood
Landmark absorption study showing iron supplements taken daily (or twice-daily) trigger hepcidin elevation that blocks subsequent absorption — supporting alternate-day dosing as more efficient for iron repletion.
Mentions calcium · 2015
Calcium intake and risk of fracture: systematic review
Bolland et al. · BMJ
Systematic review finding little evidence that increasing calcium intake prevents fractures in community-dwelling adults.
Other interactions to know
Calcium blocks thyroid medication absorption
Iron reduces levothyroxine absorption
Fluoroquinolones and tetracyclines chelate iron
Zinc and iron compete for absorption
High calcium can impair magnesium absorption
Calcium may reduce zinc absorption
Antacids significantly reduce iron absorption
PPIs reduce calcium carbonate absorption
Check your full stack in the free interaction checker.
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Medical disclaimer. This page is for educational purposes only and does not replace advice from a qualified healthcare provider.
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